This section explores optical accessories that can improve vision and comfort of use. Clip-ons and flip-ups are an alternative to prescription sunglasses. Eyeglass cases, crucial for lens care, have an interesting history and are worthy of a second look. Low-vision aids can help people with partial vision loss make the most of their remaining sight. Binoculars, telescopes and microscopes can help people expand their knowledge of the universe — whether big or small — depending on lens quality and a few other important factors.
Clip or flip!
For people who don’t want to switch between regular glasses and sunglasses, clip-ons or flip-ups are an increasingly popular answer! These sun-blocking accessories fit over prescription glasses.
Clip-ons usually attach to glasses by up to four small clamps or clips: two reaching over top of the frame; two below. The quality of this attachment system is important. Clips usually touch the lenses, which are vulnerable to scratching. Some models are attached by magnetic clips, which don’t mar the lenses but may be easier to dislodge.
If you intend to wear them a lot, invest in a good pair of clip-ons. Why cover high-quality prescription lenses with poor-quality ones?
Some brands of glasses are sold with matching clip-ons designed for an exact fit over the frame. Third-party manufacturers also supply clip-ons that will match your frame design. Custom-made models are also available. Inexpensive plastic clip-ons are sold in drug stores. These products have poor-quality lenses and clips that easily break-off or scratch expensive lenses.
Clip-ons come in a variety of materials, e.g., polycarbonate, solid tints, mirror coatings or polarized lenses. Buyers should check the manufacturer’s specifications to determine just how much ultraviolet (UV) light is blocked by a particular brand of clip-on lenses. Often, price has nothing to do with UV-blocking capability.
Flip-ups are not attached at the lens bottom but usually hang from two upper clips, floating free over the lens. A spring system enables you to flip them up and out of the way. Again, the quality of the spring system is important and one of the main factors in overall price.
Like clip-ons, flip-ups can be custom-made by third-party manufacturers. They are available in a variety of lens materials.
Flip-ups may be a better choice for baseball, cycling and other sports where people dodge between sunny and shady areas or indoors and out. Seattle Mariner Ken Griffey, Jr., has specially designed flip-ups for playing centerfield. Fishing enthusiasts can order flip-ups with magnifying lenses for fly tying.
Choose a clip-on or flip-up that fits your needs. For sports, clip-ons and flip-ups need a tight fit and firm anchoring. Wrap-around designs block more UV and bright light, but may be subject to more distortion.
Some clip-ons and flip-ups come with a thin protective case that stores easily in a glove compartment or fishing tackle box.
Since the 18th century, eyeglass cases have protected their valuable and fragile cargo from breakage, scratches and loss.
From the mid-1700s to mid-1800s, Chinese craftsmen made wooden eyeglass cases with shagreen (shark or ray hide) coverings and precious-metal mountings.
In the USA, the first cases were made from steel. Flip-top and clam-shell designs were hand-made to fit a specific pair of spectacles. Tin, brass and nickel-plated copper cases, often engraved or embossed with decorations, first appeared during the 1800s.
In the early 19th century, pressed-paper sleeves carried glasses through the Civil War era. Paper cases were custom-designed to hold spectacles for horseback riding or delicate pince-nez. Leather and leatherette-covered steel cases debuted in the early 20th century.
In Britain, eyeglass cases were first made by jewelry-case makers. By the 20th century, fabric-covered metal cases with spring lids were fashionable. Heavy-duty metal cases were essential during the war years to protect hard-to-replace eyeglasses.
Today’s selection of cases ranges from soft-bodied fabric cases with tab closures and decorative silk cases with loop-and-button fastenings to hard, burnished metal cases with soft velour linings and spring hinges. Some eye-fashion designers sell python- and ostrich-covered cases. Many eyecare professionals offer “give-away” cases inscribed with their name or yours.
Whether cases are made of hard plastic, soft vinyl, wood, leather, aluminum, cloth or precious metal, their purpose remains unchanged: to protect eyeglasses from preventable damage.
Cases are especially useful for people who frequent workshops, laboratories, construction zones or industrial areas where flecks of chemicals and glues, or wood shavings can permanently damage unshielded eyeglasses.
Boaters and outdoors enthusiasts can purchase crush-resistant cases with waterproof seals and soft interior padding. Some cases accommodate wraparound eyewear. For ease of use, some cases come with clips that secure them to belts, pockets or other objects.
Low-vision aids do not restore sight but make it easier for people with vision loss to use what sight remains. These visual devices fall into three categories: non-optical aids, simple mechanical aids and electronic aids.
Not all low-vision aids are appropriate for everyone with partial vision loss. Each person’s situation is different. Several factors influence the success of low-vision aids, including proper training, comfort and ease of use. Your eye doctor or a low-vision specialist can help you select appropriate devices and learn how to use them correctly.
Non-optical aids
Experts advise that appropriate lighting is the most important aid to good vision. They recommend the use of flexible lamps, which can be adjusted to allow light to fall directly onto the task and not into the eyes. Curtains and window blinds should be adjusted to allow daylight to fall on the task at hand.
Because people with vision loss often put a light source close to their faces, experts recommend the use of fluorescent tubes, which are cooler than hot, incandescent bulbs.
A typoscope is a dark piece of matte cardboard with an oblong, central slot. When placed over text, the typoscope frames the section to be read and eliminates glare from the surrounding white space. Although sold at low-vision resource centers, they are easily hand-made.
Reading stands raise reading material, so that people with partial vision loss don’t have to stoop over their work.
Mechanical aids
Magnifiers: From credit cards with an inset 3x magnifying lens to Sherlock Holmes-style magnifying glasses, magnifiers come in all shapes, sizes and powers. Some slip into your pocket, while others are large enough to use with an illuminated stand. Some models enlarge text from 10 to 15 times. Rectangular shapes are better for reading; round, for spotting items.
Magnifying lenses can be fit over your eyeglasses or on a headband. Since text must be held very close, experts warn that some people may find them hard to use. They can be used in conjunction with hand magnifiers.
Whether hand-held, stand-alone or eyeglass-mounted, strong magnifiers will distort images unless they have a curved (aspheric) lens. The stronger the magnifier, the smaller its field of view, i.e., the less area you will see beneath its high-powered glass or plastic lens. In poor lighting, experts recommend illuminated magnifiers.
Telescopes: For spotting street names or checking airplane departure times, hand-held or eyeglass-mounted telescopes are a handy tool, experts say. Monocle (fitted for one eye) or binocular (fitted for two eyes) telescopes may help people with low vision to see work at a distance, e.g., to read music. They can also be used for watching television. Binocular telescopes only provide low magnification. Some monocles can be adjusted for near or distance viewing.
Electronic aids
Closed circuit televisions (CCTV) have the ability to alter images electronically, improving their contrast, brightness and magnification (about 5 to 35 times) — at greater expense.
Reading matter is electronically input by a scanner or video camera, then displayed, greatly enlarged, on a television or computer monitor. Some models plug into a normal television set. In some models, the reader moves the scanner back-and-forth across the text. Other devices use a full-page document scanner. CCTVs are stationary units, usually set up at home or in the office.
Head-mounted displays are wearable electronic magnification systems, e.g., portable CCTVs. These devices capture images through a video camera, then transmit them at higher magnification to a head-mounted display unit. Many units cannot display animated images.
All binocular, telescope and microscope lenses magnify objects. How well they magnify details of distant or miniature worlds depends on lens (optical) quality.
Binoculars
The optical performance of binoculars depends on several important factors. As the characteristics of one factor may affect another, a good balance is necessary for optimal viewing.
Magnification (power) signifies the degree of enlargement. Binoculars described as 7 x 35 mm have the power to magnify objects by 7 times their normal size. Power affects image brightness; the higher the power, the darker the image. Higher powers also mean a smaller field of view and less eye relief.
Objective lens diameter (the “35 mm” in 7 x 35 mm) determines how much light enters the binoculars. Higher diameters allow people to see greater detail and image clarity. Experts recommend higher lens diameters for low light or night viewing and with high-powered lenses.
Field of view refers to the overall size of the area that’s seen through binoculars. The angle of view (in degrees) may appear on the binoculars. The linear field describes the width of the area that people see at a preset distance (in North America, 1000 yards). Generally, a smaller field of view is associated with high-powered lenses. Experts recommend larger fields of view to track fast-moving objects.
For night or astronomical viewing, exit pupil size (the size of the shaft of light transmitted through the binoculars to the eye) should match the dilation of the eye’s pupil in the dark — between 5 and 9 mm. To find exit pupil size, divide the objective lens diameter by lens power (35 mm divided by 7).
Eye relief is the distance (mm) that people can hold binoculars away from their eyes while still seeing clearly. For people who wear eyeglasses, longer or extended eye relief is critical, experts advise.
Binocular lenses may be coated with magnesium fluoride, which reduces glare. High-contrast coatings (usually amber) may enhance images. Other types of coatings may reduce eye strain.
Many binoculars are designed for a particular use, such as astronomy, marine conditions, hunting, birdwatching or viewing other sports. The choice of power, objective lens size and field of view depends on how you intend to use the binoculars. Experts advise people to choose high-quality optical lenses for better viewing.
Telescopes
Most telescopes come with a single eyepiece of low to medium power (about 25 mm). It is the eyepiece that magnifies planets, stars and other astral bodies. A wide range of eyepiece powers and designs are available. Experts recommend spending from 10% to 20% of the telescope’s cost on a set of eyepieces. Image quality is only as good as the weakest link in the optical chain, they advise.
Design rather than power is the major factor in eyepiece pricing. Less expensive designs have fewer optical parts. Two 25-mm eyepieces will provide the same magnification, but optical experts acknowledge that the eyepiece with more optical parts will generally give a better eye relief, field of view and resolution. High-quality optical parts give a crisper, more detailed image.
Experts believe that 10 to 15 times magnification is most popular range for veteran amateur astronomers. For a 10-inch telescope, most experts recommend that eyepiece powers do not exceed 500x to 600x.
Combining a low-power eyepiece with a Barlow lens gives higher magnification and better eye relief at lower cost. However, Barlow lenses do not give as sharp an image as a high-quality eyepiece alone. Experts advise people to buy the best Barlow lens they can afford, if they choose this option. A poor-quality lens will distort images and decrease the amount of light reaching the eye.
Four types of optical filters are recommended for skywatching. Experts suggest a basic set of color filters. Yellow and red filters increase contrast on planetary surfaces (e.g., Mars), blocking ultraviolet light in photographic sessions, enhancing comets and planetary cloud bands or spots. Blue and green filters cut atmospheric haze on Mars and enhance Jupiter’s Great Red Spot and Saturn’s details. Lighter-colored filters block less light in small-apertured telescopes.
Neutral-density (ND) filters block dazzling moonlight, enabling the astronomer to observe the lunar surface with less eye strain. Polarizing filters are an adjustable set of two filters that work together to dampen varying degrees of moonlight for good viewing at different lunar phases.
Light-pollution or deep-sky filters block street light but transmit light from nebulae and galaxies. Broad-band filters are the best choice for moderate light pollution, while narrow-band filters are best for high light-pollution areas.
Solar filters are absolutely essential for viewing the sun, which is one million times brighter than a full moon. Some solar filters allow people to view eclipses and sunspots safely. Most expensive filters will reveal solar flares and prominences.
Unshielded solar observation can cause complete or partial vision loss. Experts warn that looking at the sun through a colored sheet of polyester film will NOT protect people from permanent vision loss. Before use, all solar filters should be inspected for pinholes. Children should always be supervised when observing the sun.
Microscopes
A fun and educational tool, the compound microscope has two optical elements. The eyepiece (ocular) is closest to the eye, while the objective lens is closest to the object under view. Both elements determine the microscope’s power (eyepiece power multiplied by objective lens power equals magnification). The general rule is that magnification should not exceed 500 to 1000 times the numerical value of the objective lens aperture – anything more is “empty magnification”, say experts. High-powered microscopes need a brighter light source.
Eyepieces have different angles of view, e.g., wide vs. narrow field. Powers range from 5x and up. Objective lenses with wider apertures have greater resolution – an important attribute that allows the viewer to discern a greater amount of detail in specimens. The optical quality of both lenses also affects resolution.
When viewing a typical specimen, the image should not only appear larger but clearly visible in crisp, fine detail.
Benefits of high-quality lenses
With high-quality binocular, microscope or telescope lenses, anyone can truly appreciate the wonders of nature, claim optical experts. From the delicate beauty of microscopic life to spiral galaxies stretching across the immensity of the cosmos, high-quality lenses will add clarity to your view of everything under the sun.
For more information
http://www.sciencetown.com
http://www.optcorp.com
http://www.az-microscope.on.ca
